The present application is a continuation-in-part of the parent application Ser. No. 566,687 filed Dec. 29, 1983.
In any camera system, range to the object may be approximated for objects closer than the hyperfocal distance by observing the sharpness of focus of the image of the object (or a portion thereof) as the camera lens is moved or indexed across its focusing range. At the position of sharpest focus the range of the object (or portion thereof) may be read directly from a calibrated focus adjustment. This can be done whenever there is sufficient detail on the object surface or at its boundary to permit the focusing to be readily apparent to the human eye or to a processor which can determine sharpness of focus based upon fine detail. Sharpness of focus is determined when the spatial high frequency content of a region is maximized or when the percentage modulation at a region is maximized, or both. This can be achieved via many well known digital processing schemes which use the digitized output from a TV camera as input or alternatively, via the use of instantaneous holographic fourier transform techniques which instantly yield spatial frequency information. However, both techniques fail when the object has insufficient surface detail or its edges are gently curving so as to defy the requirements for the presence of some innate structure upon which to judge proper focusing.
The methods and arrangements described heretofore are for obtaining three-dimensional measurements of surfaces by observing the point at which a projected pattern was most sharply imaged. The projected pattern provides detail on a surface lacking sufficient surface detail to determine when the surface lies at the exact distance to which the projector and camera are focused. However, a surface may exhibit high curvature in certain areas. If linear patterns are projected such that the curvature is in the direction perpendicular to the projected lines, and an insufficient number of lines are able to be focused, then the distance measurement fails.